Source : Free On-Line Dictionary of Computing

hack value
     
        Often adduced as the reason or motivation for expending effort
        toward a seemingly useless goal, the point being that the
        accomplished goal is a hack.  For example, MacLISP had
        features for reading and printing Roman numerals, which were
        installed purely for hack value.  See {display hack} for one
        method of computing hack value, but this cannot really be
        explained, only experienced.  As Louis Armstrong once said
        when asked to explain jazz: "Man, if you gotta ask you'll
        never know."  (Feminists please note Fats Waller's explanation
        of rhythm: "Lady, if you got to ask you ain't got it.")